Fix incorrect setting of TaskRecord.frontOfTask. DO NOT MERGE.

When Intent.FLAG_ACTIVITY_REORDER_TO_FRONT was set the TaskRecord
member frontOfTask was being set true incorrectly for the top
activity. It should only be true for the bottom activity. This fix
ensures that frontOfTask is always set correctly for all activities by
consoldating it into one method.

Fixes bug 12171535.

Change-Id: If982dad3c81b2b816adc5d89e7e0496923098a70